1. Field of the Invention
This invention relates to electronic device processing. More particularly, this invention relates to improvements in the process of depositing tantalum-containing layers on substrates using sequential deposition techniques.
2. Description of the Related Art
The electronic device industry and the semiconductor industry continue to strive for larger production yields while increasing the uniformity of layers deposited on substrates having increasingly larger surface areas. These same factors in combination with new materials also provide higher integration of circuits per unit area on the substrate. As circuit integration increases, the need for greater uniformity and process control regarding layer characteristics rises. Formation of tantalum-containing layers, such as tantalum, tantalum nitride and tantalum silicon nitride, in multi-level integrated circuits poses many challenges to process control, particularly with respect to contact formation.
Contacts are formed by depositing conductive interconnect material in an opening (e.g., via) on the surface of insulating material disposed between two spaced-apart conductive layers. Copper is the most popular conductive interconnect material, but suffers from diffusion into neighboring layers, such as dielectric layers. The resulting and undesirable presence of copper causes dielectric layers to become conductive and ultimate device failure. Therefore, barrier materials are used to control copper diffusion.
Barrier layers formed from sputtered tantalum and reactive sputtered tantalum nitride have demonstrated properties suitable for use to control copper diffusion. Exemplary properties include high conductivity, high thermal stability and resistance to diffusion of foreign atoms. Both physical vapor deposition (PVD) and atomic layer deposition (ALD) processes are used to deposit tantalum or tantalum nitride in features of small size (e.g., about 90 nm wide) and high aspect ratios of about 5:1. However, it is believed that PVD processes may have reached a limit at this size and aspect ratio, while ALD processes are anticipated to be used in the next generation technology of 45 nm wide features having aspect ratios of about 10:1. Also, ALD processes more easily deposit tantalum-containing films on features containing undercuts than does PVD processes.
Attempts have been made to use traditional tantalum precursors found in existing chemical vapor deposition (CVD) or ALD processes to deposit tantalum-containing films. Examples of tantalum precursors may include tantalum chloride (TaCl5) and various metal-organic sources, such as pentakis(diethylamido)tantalum (PDEAT), pentakis(dimethylamido)tantalum (PDMAT), tertbutylimidotris(diethylamido)tantalum (TBTDEAT) and tertbutylimidotris(dimethylamido)tantalum (TBTDMAT). However, traditional tantalum precursors may suffer drawbacks during deposition processes. Formation of tantalum-containing films from processes using TaCl5 as a precursor may require as many as three treatment cycles using various radial based chemistries (e.g., atomic hydrogen or atomic nitrogen) to form metallic tantalum or tantalum nitride. Processes using TaCl5 may also suffer from chlorine contamination within the tantalum-containing layer. While metal-organic sources of tantalum produce tantalum-containing materials with no chlorine contamination, the deposited materials may suffer with the undesirable characteristic of high carbon content.
Therefore, there is a need for a process to deposit tantalum-containing materials into high aspect ration features having a high level of surface uniformity and a low concentration of contaminant.